indexer: check that blocks are connected

There was a rare case that a block could be incorrectly added to
the indexer if the indexer was disabled during a reorg to a height
that matched the height that was expected, and the `sync` method
for the indexer wasn't called that would detect the reorg.

lib/indexer/indexer.js

@@ -286,9 +286,20 @@ class Indexer extends EventEmitter {
     // instead of reading that information again.
     if (meta && block && view) {
       if (meta.height === this.height + 1) {
+        // Make sure that the block is connected to
+        // the indexer chain.
+        const prev = await this.getBlockMeta(this.height);
+        if (prev.hash.compare(block.prevBlock) !== 0)
+          return false;
+
         await this._addBlock(meta, block, view);
         return true;
       } else if (meta.height === this.height) {
+        // Make sure that this is the current block.
+        const current = await this.getBlockMeta(this.height);
+        if (current.hash.compare(block.hash()) !== 0)
+          return false;
+
         await this._removeBlock(meta, block, view);
         return true;
       }

test/indexer-test.js

@@ -119,6 +119,122 @@ describe('Indexer', function() {
   });
 
   describe('Unit', function() {
+    it('should connect block', async () => {
+      const indexer = new AddrIndexer({
+        blocks: {},
+        chain: {}
+      });
+
+      indexer.height = 9;
+
+      indexer.getBlockMeta = (height) => {
+        return {
+          hash: Buffer.alloc(32, 0x00),
+          height: height
+        };
+      };
+
+      let called = false;
+      indexer._addBlock = async () => {
+        called = true;
+      };
+
+      const meta = {height: 10};
+      const block = {prevBlock: Buffer.alloc(32, 0x00)};
+      const view = {};
+
+      const connected = await indexer._syncBlock(meta, block, view);
+      assert.equal(connected, true);
+      assert.equal(called, true);
+    });
+
+    it('should not connect block', async () => {
+      const indexer = new AddrIndexer({
+        blocks: {},
+        chain: {}
+      });
+
+      indexer.height = 9;
+
+      indexer.getBlockMeta = (height) => {
+        return {
+          hash: Buffer.alloc(32, 0x02),
+          height: height
+        };
+      };
+
+      let called = false;
+      indexer._addBlock = async () => {
+        called = true;
+      };
+
+      const meta = {height: 10};
+      const block = {prevBlock: Buffer.alloc(32, 0x01)};
+      const view = {};
+
+      const connected = await indexer._syncBlock(meta, block, view);
+      assert.equal(connected, false);
+      assert.equal(called, false);
+    });
+
+    it('should disconnect block', async () => {
+      const indexer = new AddrIndexer({
+        blocks: {},
+        chain: {}
+      });
+
+      indexer.height = 9;
+
+      indexer.getBlockMeta = (height) => {
+        return {
+          hash: Buffer.alloc(32, 0x00),
+          height: height
+        };
+      };
+
+      let called = false;
+      indexer._removeBlock = async () => {
+        called = true;
+      };
+
+      const meta = {height: 9};
+      const block = {hash: () => Buffer.alloc(32, 0x00)};
+      const view = {};
+
+      const connected = await indexer._syncBlock(meta, block, view);
+      assert.equal(connected, true);
+      assert.equal(called, true);
+    });
+
+    it('should not disconnect block', async () => {
+      const indexer = new AddrIndexer({
+        blocks: {},
+        chain: {}
+      });
+
+      indexer.height = 9;
+
+      indexer.getBlockMeta = (height) => {
+        return {
+          hash: Buffer.alloc(32, 0x01),
+          height: height
+        };
+      };
+
+      let called = false;
+      indexer._removeBlock = async () => {
+        called = true;
+      };
+
+      const meta = {height: 9};
+      const block = {hash: () => Buffer.alloc(32, 0x02)};
+      const view = {};
+
+      const connected = await indexer._syncBlock(meta, block, view);
+      assert.equal(connected, false);
+      assert.equal(called, false);
+    });
+
     it('should not index transaction w/ invalid address', async () => {
       const indexer = new AddrIndexer({
         blocks: {},